Credit Quality Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Troubled Debt Restructuring
Line of credit commitments for modified troubled debt restructurings	$ 46	$ 39
Letter of credit commitments for modified troubled debt restructurings	22	23
Mortgage Loans In Process Of Foreclosure Amount	$ 290	$ 303

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL49126937-111524

Name:	us-gaap_MortgageLoansInProcessOfForeclosureAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant